As a brake cable connecting device for a drum brake, a forward-pull type parking brake device is known wherein a brake cable is connected to a free end of a brake lever in the drum brake while a base end of the brake lever is pivotally mounted on a shoe web of one of the brake shoes.
The brake cable that activates the brake lever by being pulled from a distance is comprised mainly of an inner cable and an outer casing. At the free end of the brake lever, there is provided with a cable retaining groove bent into U-shape in cross section. One end of the inner cable is connected to a brake application device such as a hand lever in a driver's compartment, and the other end of the inner cable is inserted into the drum brake through an opening in a back plate and is fit in the cable retaining groove of the brake lever.
When an enlarged cable end fixed to the other end of the inner cable engages on an edge surface of the cable retaining groove opposite to a cable pulling direction, the brake cable is completely installed in the cable retaining groove. When the hand lever is operated in the driver's compartment, the inner cable is pulled accordingly, which rotates the brake lever to open a pair of brake shoes to activate the parking brake.
In a brake device of this kind, when the brake cable is pre-installed, several disadvantages are incurred such as a problem of maintaining associated parts, increase in space required for transportation, and/or damages in the brake cable or other components. Thus, it is desirable not to install the brake cable in the assembly process of the brake device, but to do it during the assembly process of the automobile.
However, in general, the brake lever in the drum brake is arranged under the shoe web of the brake shoe, i.e., the back plate side of the shoe web, which makes it difficult to engage the cable end with the brake lever. After the drum brake is covered with the brake drum, it becomes further difficult to specify the location of the brake device to install the brake cable.
Therefore, the connecting device for easily fastening the brake cable to the brake lever is proposed in the U.S. Pat. No. 5,002,159. In this patent, a guide pipe having a curved shape is fixed to an opening of the back plate where also an outer casing of the brake cable is connected so that the cable end passing through the guide pipe is aligned in the cable retaining groove of the brake lever.
However, in the brake cable connecting device disclosed in this patent, in order to align the cable end accurately in the cable retaining groove of the brake lever, the guide pipe must be extended to be close enough to the cable retaining groove. When the space between the end of the guide pipe and the cable retaining groove is decreased, it causes a problem that the brake lever interferes with the guide pipe during its operation. Therefore, it is difficult to compromise both requirements described above.
The assignee of this invention proposed an improved version of the brake cable connecting device which is disclosed in the Japanese Patent Laid Open Publication No. 10-220506. This conventional device is reproduced in FIGS. 8 and 9 and described below.
FIG. 8 is a plan view showing a leading-trailing type (hereinafter "LT type") drum brake and FIG. 9 is a perspective view showing an essential portion of the brake cable connecting portion of FIG. 8. As shown in FIG. 8, brake shoes 1 and 2 arranged symmetrically at right and left in the brake device have a structure identical to each other and comprise crescent-shaped shoe webs 1a and 2a and shoe rims 1b and 2b connected respectively in T-shape in cross section. Brake linings 1c and 2c are respectively adhered to the outer surfaces of the shoe rims 1b and 2b.
The brake shoes 1 and 2 are elastically supported on a back plate 5 by shoe hold means 3 and 4. The lower adjacent ends of the brake shoes 1 and 2 are abutted against an anchor member and are limited to be lifted from the back plate 5 by a retaining plate 6. Further, the upper adjacent ends of the brake shoes 1 and 2 are respectively engaged with corresponding pistons of a wheel cylinder 7.
Between the brake shoes 1 and 2, an upper shoe return spring 8 and a lower shoe return spring 9 are respectively provided so as to urge the pair of brake shoes 1 and 2 toward each other. Between the brake shoe 1 and a brake lever 10 is provided with an adjuster 13 to be able to adjust the clearance between the brake drum (not shown) and the brake shoes 1 and 2.
The brake lever 10 is superposed under the shoe web 2a of the brake shoe 2. A base end of the brake lever 10 is rotatably supported on the shoe web 2a with a pin 11 as the fulcrum. A lever return spring 12 arranged between the shoe web 2a and the brake lever 10 applies a rotational force to the brake lever 10 with a pivotal point of the pin 11 in a clockwise direction (non-operational position).
FIG. 9 shows the structure in the vicinity of the free end of the brake lever 10 as viewed from the back plate 5 side. A cable retaining groove 10b, a guide member 10c, and a projection 10e are integrally formed on the free end portion of the brake lever 10. The cable retaining groove 10b has a U-shape for retaining an inner cable 14 that constitutes a brake cable. The guide member 10c is projected toward the cable pulling direction (hereafter "front", "front side" or "forward") from the body side of the cable retaining groove 10b. The projection 10e is formed on a turn-up portion 10d of the cable retaining groove 10b and projected toward the direction opposite to the cable pulling direction (hereafter "back", "backside" or "backward").
The guide member 10c of the brake lever 10, constituting a cable guide means, is formed in a fan-like shape which is widened toward the tip thereof and has a surface of partially conical or pyramidal. When a cable end 14a contacts anywhere on the surface of the widened end of the guide member 10c, it can be securely guided to the engagement position along the partially conical or pyramidal surface. A ramped surface 10f rising backwardly upwardly is formed on the marginal edge of the turn-up portion 10d for bending the inner cable 14 into contact with the cable end 14a upon advancing the cable end 14a thereon.
The connecting procedure of the brake cable is explained in the following. When the inner cable 14 passes through a guide pipe 16 which acts as a cable deflection means from outside (brake outside) of the back plate 5, the cable end 14a is guided toward the guide member 10c of the brake lever 10 facing the guide pipe 16.
When the inner cable 14 is pushed further in the backward direction, the cable end 14a is guided from the guide member 10c to the ramped surface 10f of the turn-up portion 10d. When the cable end 14a advances further on the ramped surface 10f while it bends the inner cable 14 upwardly along to the angle of the ramped surface 14f, thereby generating a downward return force in the inner cable 14, the tip of the cable end 14a eventually reaches a plate spring 17. The cable end 14a further advances while deforming the plate spring 17.
After the cable end 14a passes the projection 10e, the inner cable 14 immediately moves downward into the cable retaining groove 10b by the downward return force thereof as well as a return force of the plate spring 17. Consequently, the cable end 14a is captured by the backside edge of the cable retaining groove 10b. Because the cable end 14a goes down as noted above, the plate spring 17 returns to its original state by the return force produced by an elastic portion 17a. At this time, a hitting sound is generated because a clash portion 17b of the plate spring 17 hits the side surface of the brake lever 10. Thus, a worker can confirm by this sound that the cable connection has been completed.
After the connecting procedure noted above, the inner cable 14 may move backward along an inner surface of the shoe rim 2b of the brake shoe 2. Such a movement of the inner cable 14 is suppressed by the plate spring 17 in such a way that the lower (free) end of the elastic portion 17a of the plate spring 17 prevents the inner cable 14 from coming out from the cable retaining groove 10b. Thus, the connection of the inner cable 14 and the brake lever 10 is maintained. The gap between the lower end of the plate spring 17 and the tip of the projection 10e is made smaller than the diameter of the cable end 14a, thereby further prohibiting the cable end 14a from coming out from the cable retaining groove 10b.
In the case where the cable end 14a has to be taken out from the brake lever 10, such as when the brake shoes 1 and 2 are to be replaced, the plate spring 17 may be forcibly deformed backwardly to create an enough clearance to pass the cable end 14a.
According to the configuration of the brake device described in the foregoing, the inner cable and the cable end can be securely connected to the brake lever even in the case that the brake lever is located under the shoe web facing the back plate or the brake cable is required to be blind connection after the brake drum is installed, and thus invisible to a worker. Moreover, the completion of the brake cable connection can be confirmed by the hitting sound produced by the plate spring. Once connected to the brake lever, the inner cable or the cable end will not disconnected from the brake lever unless the plate spring is manually and forcibly deformed.
In the conventional brake device described above, since the brake lever 10 withstands a large force, the brake lever generally has to be made of thick steel. In the foregoing example, since it is integrally made with the brake lever 10, the guide member 10c also has the same thickness of the brake lever 10. However, once used for installing the brake cable, the guide member 10c plays no other role thereafter. Further, it is sufficient that the guide member 10c can guide the cable end 14a toward the predetermined location. Thus, the guide member 10c needs not to have so much mechanical strength.
Since the guide member 10c is made of the steel with the same thickness of the brake lever 10, it also has significant weight. In the automobile industry, there is a strong demand for weight reduction in any components used in automobiles. Further, because of the integration of the guide member 10c, the shape of the brake lever 10 has to be complicated, thereby limiting design flexibility, increasing material cost and processing cost, resulting in increase of an overall manufacturing cost.
As to the guide pipe 16 functioning as the cable deflecting means, the inner cable 14 which slides along the inner wall of the guide pipe 16 receives a high tension when the brake is activated. Because the guide pipe 16 is curved rather than straight, the part of the tension (tensile force) is applied to the curved portion of the guide pipe 16. Thus, the guide pipe 16 must have sufficient thickness to ensure sufficient mechanical strength and be firmly fixed to the back plate 5 by means of, for example, welding. Further, the guide pipe 16 must have sufficient length to accurately guide the cable end 14a to the guide member 10c. Because of the foregoing reasons, the guide pipe 16 in the prior art is heavy and costly.